Research Articles (School for Science and Technology)

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Analysis of heat transfer in Berman flow of nanofluids with Navier slip, viscous dissipation, and convective cooling
(Hindawi Publishing Corporation, 2014-03-31) Makinde, O. D.; Khamis, S.; Tshehla, M. S.; Franks, O.
Heat transfer characteristics of a Berman flow of water based nanofluids containing copper (Cu) and alumina (Al2O3) as nanoparticles in a porous channel with Navier slip, viscous dissipation, and convective cooling are investigated. It is assumed that the exchange of heat with the ambient surrounding takes place at the channel walls following Newton’s law of cooling. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using appropriate similarity transformations. These equations are solved analytically by regular perturbation methods with series improvement technique and numerically using an efficient Runge-Kutta Fehlberg integration technique coupled with shooting scheme.The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, pressure drop, and Nusselt numbers are presented graphically and discussed quantitatively.
Analysis of thermal stability in a convecting and radiating two-step reactive slab
(Hindawi, 2013) Makinde, O. D.; Tshehla, M. S.
This paper investigates the combined effects of convective and radiative heat loss on thermal stability of a rectangular slab of combustible materials with internal heat generation due to a two-step exothermic chemical reaction, taking the diffusion of the reactant into account and assuming a variable (temperature dependent) preexponential factor. The nonlinear differential equation governing the transient reaction-diffusion problem is obtained and tackled numerically using a semidiscretization finite difference technique. A special type of Hermite-Pade approximants coupled with perturbation technique are employed to analyze the effects of ´ various embedded thermophysical parameters on the steady state problem. Important properties of the temperature field including thermal stability conditions are presented graphically and discussed quantitatively.
Application of successive linearisation method to squeezing flow with bifurcation
(Hindawi Publishing Corporation, 2014-01-02) Motsa, S. S.; Makinde, O. D.; Shateyi, S.
This paper employs the computational approach known as successive linearization method (SLM) to tackle a fourth order nonlinear differential equation modelling the transient flow of an incompressible viscous fluid between two parallel plates produced by a simple wall motion. Numerical and graphical results obtained show excellent agreement with the earlier results reported in the literature. We obtain solution branches as well as a turning point in the flow field accurately. A comparison with numerical results generated using the inbuilt MATLAB boundary value solver, bvp4c, demonstrates that the SLM approach is a very efficient technique for tackling highly nonlinear differential equations of the type discussed in this paper.
The background radiation and exposure levels at various South African west coast military units
(Stellenbosch University. Faculty of Military Science (Military Academy), 2014) Bezuidenhout, Jacques
The West Coast of South Africa between St Helena Bay to the north and Langebaan Lagoon to the south is characterised by numerous granite protrusions. These outcrops are elements of the underlying Cape Granite Suite, which forms the bedrock of a large part of the Western Cape. Granite contains high levels of natural radionuclides, which results in high levels of natural background radiation in the surrounding area. The impacts of these high levels of radiation exposure on military personal are of concern. There are four military units located in this part of the West Coast, namely SAS Saldanha, 4 Special Forces Regiment, Langebaan Road Air Force Base and the Military Academy. Different sites in and around these military units were selected and soil samples were taken. Laboratory gamma ray measurements were done to determine the levels of natural radioactive nuclides in the soil samples. The radioactive nuclide concentrations were interpolated and then mapped with the help of geographic information systems (also known as geospatial information systems or GIS) software. An evaluation of the annual dose rate of military personnel at the units on the West Coast was made and found to range between 0,017 mSv/y and 0,163 mSv/y. These values were mapped and compared to the average global annual dose rate of 0,070 mSv/y. This article reports on an investigation of these results and the overall exposure levels of personnel from the various military units on the West Coast of South Africa.
Computational dynamics of arterial blood flow in the presence of magnetic field and thermal radiation therapy
(Hindawi Publishing Corporation, 2014-04-22) Chinyoka, T.; Makinde, O. D.
We conduct a numerical study to determine the influence of magnetic field and thermal radiation on both velocity and temperature distributions in a single blood vessel. The model here assumes that blood is a Newtonian incompressible conducting fluid with radially varying viscosity due to hematocrit variation. The transient equations of momentum and energy transport governing the flow in an axisymmetric configuration are solved numerically using a semi-implicit finite difference method. Results are presented graphically and discussed both qualitatively and quantitatively from the physiological point of view. The results of this work may enhance current understanding of the factors that determine the effects of hyperthermia treatment on tumor tissues.
Computational modelling and similarity reduction of equations for transient fluid flow and heat transfer with variable properties
(Hindawi, 2013) Moitsheki, R. J.; Makinde, O. D.
We consider a system of coupled partial differential equations describing transient fluid flow and heat transfer with variable flow properties. Classical Lie point symmetry analysis of this system resulted in admitted large Lie algebras for some special cases of the arbitrary constants and the source term. Symmetry reductions are performed and as such the system of partial differential equations is reduced to the system of ordinary differential equations. Some reduced ordinary differential equation could be solved exactly with restrictions on the parameters appearing in it. In addition, shooting quadrature is employed to numerically tackle the nonlinear model boundary value problem and pertinent results are presented graphically and discussed quantitatively
Effect of the elemental content of shells of the bivalve mollusks (Mytilus galloprovincialis) from Saldanha Bay (South Africa) on their crystallographic texture
(MDPI, 2021) Nekhoroshkov, Pavel; Zinicovscaia, Inga; Nikolayev, Dmitry; Lychagina, Tatiana; Pakhnevich, Alexey; Yushin, Nikita; Bezuidenhout, Jacques
A both wild and farmed mussels in natural conditions, anthropogenic inputs are usually reflected in the increase of the content of specific elements. To determine the possible effect of the elemental patterns of farmed and wild mussels (Mytilus galloprovincialis) collected in the Saldanha Bay area (South Africa) on the crystallographic texture of the shells, the content of 20 elements in shells and 24 in the soft tissue of mussels was determined by neutron activation analysis. The crystallographic texture of mussel shells was analyzed using time-of-flight neutron diffraction. The wild mussels from open ocean site live in stressful natural conditions and contain higher amounts of the majority of determined elements in comparison with mussels farmed in closed water areas with anthropogenic loadings. The changes between the maximums of the same pole figures of the three samples are in the range of variability identified for the genus Mytilus. The content of Cl, Sr, and I was the highest in mussels from the open ocean site, which is reflected by the lowest mass/length ratio. The determined crystallographic textures of mussels are relatively stable as shown in the analyzed pole figures despite the concentrations of Na, Mg, Cl, Br, Sr, and I in shells, which significantly differ for wild and farmed mussels. The stability of the crystallographic texture that we observed suggests that it can be used as a reference model, where if a very different texture is determined, increased attention to the ecological situation should be paid.
Estimation of radon potential through measurement of uranium concentrations in granite geology
(Academy of Science of South Africa, 2019) Bezuidenhout, Jacques
The geology of an area can be used as a predictor for radon potential. Granite rock typically contains a high concentration of uranium and subsequent elevated emanation of radon gas. The geology of the western part of the Western Cape Province in South Africa is dominated by granite bedrock but very few studies on radon have been conducted in this area. Uranium concentrations were consequently measured on a large granite hill in the Saldanha Bay area of the Western Cape and a relationship between indoor radon and uranium concentrations was used to model radon potential on the outcrop. Results from granite rich environments in India were modelled in order to extract a relationship between indoor radon concentrations, radon exhalation rates and uranium concentrations. Radon exhalation rates greater than 0.35 Bq/m2h were predicted and estimated indoor radon concentrations in excess of 400 Bq/m3 were also predicted for the hill. The modelled results were compared with indoor radon measurements taken in the town of Paarl in the Western Cape, which sits on the same granite bedrock formation. The predicted radon potential correlated well with the physical measurements.
The flow of a variable viscosity fluid down an inclined plane with a free surface
(Hindawi, 2013) Tshehla, M. S.
The effect of a temperature dependent variable viscosity fluid flow down an inclined plane with a free surface is investigated.The fluid film is thin, so that lubrication approximation may be applied. Convective heating effects are included, and the fluid viscosity decreases exponentially with temperature. In general, the flow equations resulting from the variable viscosity model must be solved numerically. However, when the viscosity variation is small, then an asymptotic approximation is possible. The full solutions for the temperature and velocity profiles are derived using the Runge-Kutta numerical method.The flow controlling parameters such as the nondimensional viscosity variation parameter, the Biot and the Brinkman numbers, are found to have a profound effect on the resulting flow profiles.
Influence of rotation on transversely isotropic piezoelectric rod coated with a thin film
(Polish Academy of Sciences, 2018) Selvamani, Rajendran; Makinde, Oluwole Daniel
In this paper, the influence of rotation on axisymmetric waves of a piezoelectric rod coated with a thin film is studied using constitutive form linear theory elasticity and piezo-electric equations. Potential functions are introduced to uncouple the equations of motion in radial and axial directions. The surface area of the rod is coated by a perfectly conducting material. The frequency equations are obtained for longitudinal and flexural modes of vibration and are studied numerically for PZT-4 ceramics. The computed non-dimensional frequency, phase velocity, relative frequency shift, electromechanical coupling and electric displacement are presented in the form of dispersion curves. This type of study is important in the construction of rotating sensors and gyroscope.
The investigation of radionuclides distributions in beach sand by means of GIS techniques
(CONSAS Conference, 2015-11) Bezuidenhout, Jacques
A transportable and robust gamma ray detection system (GISPI) was employed to determine the concentrations of naturally occurring radionuclides on various beaches in and around Saldanha Bay, located on the West Coast of South Africa. Several mathematical techniques were applied to obtain GIS overlay that could be used to investigate various geophysical phenomenon. The results demonstrated direct relationships between radionuclide concentrations, grain size of beach sediment and the intensity of wave action. The element concentrations were used to make deductions on the origin of some of the beach sand. The article finally draws conclusions on coastal and beach formation processes, based on the results of the distribution of various radionuclides.
The mapping and investigation of radionuclide pollution in the processing plant of a spent phosphate mine by using GIS techniques
(CONSAS, 2018) Bezuidenhout, Jacques
The mining and refinement of phosphate is characterised by high levels of uranium. An in situ gamma ray survey was done at the processing plant of a spent phosphate mine near Vredenburg on the west coast of South Africa in order to assess radionuclide concentrations. The concentrations of potassium, thorium and radioactive progeny of uranium were measured and plotted with the help of QGIS software. The results demonstrated high concentrations in specific areas of the plant. The highest concentrations were found to be 898 Bq/kg for potassium, 162 Bq/kg for 232Th and 639 Bq/kg for 226Ra. It was demonstrated that the refinement process technologically enhanced the naturally occurring radioactive nuclides and contaminated sections of the processing plant. The causes of the contamination were also investigated. The effective dose for the various parts of the processing plant was also estimated and the highest level was found to be 0.45 mSv/y. The article finally draws conclusions as to the environmental impact of the radiation and possible future preventative measures that could be followed in order to minimize pollution.
Mapping of historical human activities in the Saldanha Bay military area by using in situ gamma ray measurements
(Faculty of Military Science, Stellenbosch University, 2012) Bezuidenhout, Jacques
Saldanha Bay on the west coast of South Africa is surrounded by various nature reserves, military units and training sites. Over a long period of time, large parts of this semi-arid area were exposed to human activities, including military training and the preparation of forces for war. This article investigates the prospect of identifying areas where human activities took place via mapping of the variation in primordial radioactive isotopes. For this purpose, in situ gamma-ray data were obtained from selected locations around Saldanha Bay. The data were used to extract concentrations of primordial radioactive isotopes in these locations. The radioactive primordial isotope concentrations were then mapped and compared to historical evidence of human activities in these areas. The concentrations of potassium isotope showed a relationship to the height above mean sea level. Historical human activities were mainly confined to flatter regions of the area around Saldanha Bay and therefore also relate to the height above mean sea level. The potassium concentrations and the areas where human activities took place were compared and a significant relationship was found.
Natural convection of viscoelastic fluid from a cone embedded in a porous medium with viscous dissipation
(Hindawi, 2013) Makanda, Gilbert; Makinde, O. D.; Sibanda, Precious
We study natural convection from a downward pointing cone in a viscoelastic fluid embedded in a porous medium. The fluid properties are numerically computed for different viscoelastic, porosity, Prandtl and Eckert numbers.The governing partial differential equations are converted to a system of fourth order ordinary differential equations using the similarity transformations and then solved together by using the successive linearizationmethod (SLM).Many studies have been carried out on natural convection from a cone but they did not consider a cone embedded in a porous medium with linear surface temperature. The results in this work are validated by the comparison with other authors.
New developments in fluid mechanics and its engineering applications
(Hindawi, 2013) Makinde, Oluwole Daniel; Khan, Waqar Ahmed; Chinyoka, Tirivanhu
Fluid mechanics is an active field of research with many unsolved or partially solved problems in science and engineering. Fluid mechanics can be mathematically complex. Sometimes the problems can best be solved by numerical methods, typically using computers. Fluids have the ability to transport matter and its properties as well as transmit force; therefore fluidmechanics is a subject that is particularly open to cross-fertilization with other sciences and disciplines of engineering. The subject of fluidmechanics is highly relevant in such domains as mechanical, chemical, petrochemical, civil, metallurgical, biological, and ecological engineering.
New interventions and sustainable solutions : reappraising illegal artisanal mining in South Africa
(University of Cape Town, Centre of Criminology, 2018) Mkhize, Mbekezeli Comfort
Despite being recognised as a significant contributor in the South African economy, the mining industry is riddled with illegal mining activities. Though it remains difficult to precisely measure the extent of the activities in financial terms, it is estimated that more than R72 Billion have been lost. Lack of research on illegal mining partly compounds the problem. In view of this knowledge-gap, this article argues that whilst there is a multiplicity of stakeholders who deal directly with unlawful activities, poor integration of capacities at different levels remain discernible. The article assesses available literature and employs two theoretical perspectives as lenses through which to view the underlying reasons and the measures that can be put in place to quell illegal mining. The article concludes that an integrated model needs to be put in place in order to quell illegal mining in South Africa. The article recommends that the resources need to be pulled together and collaborative efforts need to be enhanced at all levels.
Nonlinear fluid flow and heat transfer
(Hindawi Publishing Corporation, 2014-06-24) Makinde, O. D.; Moitsheki, R. J.; Jana, R. N.; Bradshaw-Hajek, B. H.; Khan, W. A.
No abstract.
Optimal control of HIV/AIDS in the workplace in the presence of careless individuals
(Hindawi Publishing Corporation, 2014-06-26) Seidu, Baba; Makinde, Oluwole D.
A nonlinear dynamical system is proposed and qualitatively analyzed to study the dynamics of HIV/AIDS in the workplace. The disease-free equilibrium point of the model is shown to be locally asymptotically stable if the basic reproductive number, R0, is less than unity and the model is shown to exhibit a unique endemic equilibrium when the basic reproductive number is greater than unity. It is shown that, in the absence of recruitment of infectives, the disease is eradicated when R0 < 1, whiles the disease is shown to persist in the presence of recruitment of infected persons. The basic model is extended to include control efforts aimed at reducing infection, irresponsibility, and nonproductivity at the workplace. This leads to an optimal control problem which is qualitatively analyzed using Pontryagin’s Maximum Principle (PMP). Numerical simulation of the resulting optimal control problem is carried out to gain quantitative insights into the implications of the model. The simulation reveals that a multifaceted approach to the fight against the disease is more effective than single control strategies.
Unsteady hydromagnetic flow of radiating fluid past a convectively heated vertical plate with the Navier slip
(Hindawi Publishing Corporation, 2014-04-17) Makinde, O. D.; Tshehla, M. S.
This paper investigates the unsteady hydromagnetic-free convection of an incompressible electrical conducting Boussinesq’s radiating fluid past a moving vertical plate in an optically thin environment with the Navier slip, viscous dissipation, and Ohmic and Newtonian heating. The nonlinear partial differential equations governing the transient problem are obtained and tackled numerically using a semidiscretization finite difference method coupled with Runge-Kutta Fehlberg integration technique. Numerical data for the local skin friction coefficient and the Nusselt number have been tabulated for various values of parametric conditions. Graphical results for the fluid velocity, temperature, skin friction, and the Nusselt number are presented and discussed. The results indicate that the skin friction coefficient decreases while the heat transfer rate at the plate surface increases as the slip parameter and Newtonian heating increase.

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